Gingrich, a former House speaker from Georgia, told CBS' "Early Show" he thinks Romney, a former Massachusetts governor, is a "liar" for not taking responsibility for the barrage of negative ads put on Iowa television by a super political action committee.

"This is a man whose staff created the PAC. His millionaire friends fund the PAC. He pretends he has nothing to do with the PAC. It's baloney," Gingrich said.

"He's not telling the American people the truth. It's just like his pretense that he's a conservative. Here's a Massachusetts moderate who has tax-paid abortions in Romneycare; puts Planned Parenthood in Romneycare; raises hundreds of millions of dollars of taxes on businesses; appoints liberal judges to appease Democrats; and wants the rest of us to believe somehow he's magically a conservative."

Asked about an earlier comment in which he said, "Somebody who will lie to you to get to be president will lie to you when they are president," Gingrich reaffirmed his assertion Romney is a liar.

That doesn't mean, however, Romney won't get Gingrich's vote if he becomes the Republican presidential nominee.

Gingrich posited Romney wouldn't stand a chance against President Obama but said he'd stand behind the former Massachusetts governor if that's what it came down to.

"Do you really want a Massachusetts moderate who won't level with you to run against Barack Obama who, frankly, will just tear him apart? I mean, he will not survive against the Obama machine," Gingrich said, adding, "I would support him against Barack Obama. … I would support a Republican candidate against Barack Obama because I think Barack Obama is tearing the country apart."

Gingrich said he's looking forward to the next couple of debates -- where he has shined this election cycle -- and said Iowa was still up for grabs.

"There are a large number of undecided people who walk in genuinely interested and tell you up front they haven't made their mind up. I think anybody could come in first," he said.

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